[LinuxBIOS] How to study the source code...?

[Huang-Jen Wang]

Dear all,
Recently I am studying the source code , because I want to try to 
porting new mainboard later, but  it is not easy to realize source code
I begin my study  from the src/southbridge/amd8111/amd8111.c
There are some lines that I can't understand even I have amd8111
datasheet....hope you can tell me

1.devfn = bus_dev->path.u.pci.devfn + (1 << 3); 
2.index = ((dev->path.u.pci.devfn & ~7) >> 3) + 8;
3.devfn = (dev->path.u.pci.devfn) & ~7;

Thanks  advanced...

HJ Wang